1. Field of the Invention
The invention is directed to a photo-stable coating. In particular, the invention is an antimicrobial photo-stable composition used for coating a variety of medical materials. The invention also contemplates methods of making such composition, methods of forming coatings on medical materials and medical materials coated with the coating composition.
2. Description of the Related Art
Throughout this application, various references are cited in parentheses to describe more fully the state of the art to which this invention pertains. The disclosure of these references are hereby incorporated by reference into the present disclosure.
Anti-microbial agent(s) such as acetohydroxamic acid and magnesium ammonium phosphate hexahydrate have been added to a surface polymer coating as is disclosed for example in U.S. Pat. No. 5,788,687.
Silver is known to have general anti-microbial properties directed against a wide range of bacteria and fungi and has been used for many years in clinical settings and on medical devices which include coatings for catheters, cuffs, orthopedic implants, sutures, dental amalgams and wound dressings. Silver has been demonstrated to reduce the incidence of infection associated with the use of such devices. Silver alloy and silver oxide have been used to coat urinary catheters and are somewhat effective in preventing urinary tract infections.
The general use of silver as a prophylactic against infection has not found widespread application because of problems associated with the inadequate coating of device surfaces. Such problems include: poor solubility of metallic silver and silver oxides; short half-life; rapid binding of silver ions; inactivation by proteins; light-mediated inactivation and discoloration; and slow release of silver ions from the metallic complex. While not subscribing to any particular theory, colorless cationic silver may be photoreduced to metallic silver with subsequent dark discoloration. The ensuing discoloration of the ionic silver when coated onto medical devices results in undesirable coloration of the material or surface of the device.
U.S. Pat. No. 4,646,730 discloses polyvinylpyrrolidone (PVP)/silver sulfadiazine hydrogel dressings, where the gel is formed by utilizing electron beam irradiation to crosslink the PVP. Photo-stabilization of the silver component is accomplished by adding magnesium tri-silicate to the gel and by also adding hydrogen peroxide and/or polyacrylic acid.
U.S. Pat. No. 6,468,521 discloses a stabilized silver composition in which the silver compound is a complex with a primary, secondary or tertiary amine and the complex is associated with a hydrophilic polymer.
U.S. Pat. Nos. 4,906,466 and 5,413,788 disclose antimicrobial silver compositions in which photo-stability is enhanced by use of titanium oxide.
U.S. Pat. No. 6,669,981 discloses methods for enhancing the photo-stability of silver comprising an organic solution containing silver where the silver is subsequently photo-stabilized by treatment with ammonia, ammonium salts, thiosulfates, chlorides and/or peroxides.
Nomiya et al. (Inorganic Chemistry: 39:3301-3311, 2000) disclose the synthesis of water-soluble silver-pyrrolidone carboxylic acid (silver-PCA) complexes with antimicrobial activity. The material so produced shows discoloration caused by photoreduction of the silver-PCA complex.
JP 2001335405 and JP 2000256365 describe compounds that form a photostable complex with silver. The most effective was a silver-2-pyrrolidone-5-carboxylic acid complex (silver-PCA). However, photo-reduction and discoloration of the complex remains a problem.
There remains a need to develop a hydrophilic silver-complex that deters photo-induced discoloration of the silver-PCA complex on the surface of medical devices such as catheters, wound dressings and the like.